Influence of textural and wettability variations on predictions of DNAPL persistence and plume development in saturated porous media

Abstract

Numerical simulations examine the migration, entrapment, and mass recovery behavior of DNAPLs in aquifer systems with coupled textural and wettability variations. Permeability fields of varying degrees of heterogeneity (i.e., differing σ ln( k) 2) were generated with sequential Gaussian simulation, using geostatistical parameters derived from core grain size measurements in a sandy glacial outwash aquifer. Organic-wet mass fraction, a representative metric for wettability, was correlated to porous media permeability. A multiphase flow simulator incorporating wettability-dependent constitutive relationships for capillary behavior is used to generate residual saturation distributions for tetrachloroethene (PCE) spill events in these synthetic aquifers. Simulated saturation distributions then serve as initial conditions for compositional simulations of PCE dissolution, to examine the effect of coupled wettability and permeability variations on DNAPL mass recovery. Simulations reveal considerable differences in predicted depth of organic liquid penetration, extent of vertical spreading, and magnitude of maximum entrapped saturation for the various modeled scenarios. These differences are directly linked to observable variations in effluent concentration and mass recovery predictions in the aqueous phase flushing simulations. Results suggest that mass recovery behavior may be highly realization dependent and not closely correlated with geostatistical parameters.